Deformation image development apparatus



Dec. 22, 1964 H. c. MEDLEY DEFORMATION IMAGE DEVELOPMENT APPARATUS Filed Oct. 2. 1961 Will/11M INVENTOR, HAROLD C. MEDLEY FIG. 2

ATTORNEY United States Patent ()fiice 3,162,104 Patented Dec. 22, 1964 The invention relates to electrophotography, and it particularly pertains to the development of deformation images on dielectric material.

There is a known method of thermoplastic deformation image recording using a film comprising a transparent conductive layer base on which is laid a very thin layer of low melting point thermoplastic material. The film is subjected to a scanning electron beam which charges the thermoplastic surface with a pattern corresponding to the image to be recorded. Immediately thereafter, the conductive layer is heated for a very short time by passing electric current through it. The heating softens the thermoplastic, and the electrostatic forces between the charged thermoplastic surface and the conductive coating create depressed areas in the thermoplastic surface in accordance with the charge pattern. The film is then cooled and the depression or deformation pattern is fixed. By means of a Schlieren optical system, an optical image may be projected on a large screen, producing a dark screen except to those areas of the film where the light beam is refracted by the sloping sides of the surface depression. According to the known technique, the beam scanning and heating are both carried out in a high vacuum. The heating is very critical and has been one of the severest development problems.

An object of the problem is to obviate the need for a high vacuum chamber for exposing, developing and fixing a film for producing a deformation image.

Another object of the invention is to provide a method of developing a deformation image on dielectric film, ob viating the critical heating problem.

A latent electrostatic image formed on a film of dielectric material by known techniques is developed according to the invention by exposing the soluplastic dielectric material to a solvent vapor, causing the plastic to soften and thereby producing a deformation image by action of the electrostatic forces. Development is halted and the image solidified merely by removing the plastic dielectric film from contact with the vapor, allowing the solvent to evaporate from the plastic film. Preferably the vapor is purged from the plastic by a blast of air or other gas which does not affect the plastic film dielectric material.

Apparatus for carrying outa process according to the invention comprises in one form a print frame of boxlike structure connected in a vapor tight system to a container of solvent from which vapor is obtained. The charged film of dielectric material is placed in the print frame and solvent vapor is directed into the film to soften it. A condenser for condensing the excess vapor after the developing process is connected tothe box-like structure for returning the excess solvent to the container. Prefen ably, forced air is applied for movement of the vapor and the air is also used to purge excess vapor from the film. Apparatus for automatically and continuously carrying out a process according to the invention comprises in one form a rotatable drum electrostatic image transfer device of the prior art from which the charged delectric film is taken and, according to the invention, led over another drum to expose the film first in a chamber containing solvent vapor, and then in anotherchamber wherein clear air is injected to purge the excess vapors from the film and fix the film negative. Condensing means are connected to the two chambers to condense excess vapor and return the condensed solvent to the source tank.

In order that full advantage of the invention may be readily obtained in practice, preferred embodiments of the invention, given by way of example only, are described in detail hereinafter with reference to the accompanying drawing forming a part of the specification, and in which:

FIG. 1 illustrates simple apparatus for carrying out a 7 process of vapor solvent development of dielectric material charged image patterns according to the invention; and

FIG. 2 illustrates apparatus for carrying out the process of the invention in an automatic and continuous mode of operation.

FIG. 1 depicts the essentials of apparatus for carrying out a method according to the invention for developing latent electrostatic images formed on dielectric material. An electrostatic image, corresponding to a desired document is first formed by conventional means on a known medium, for example, as shown and described in U.S. patent application Serial No. 127,725, filed on July 28, 1961, by Harold Clinton Medley and Roland Michael Schatfert for Electrostatic Image Transfer Processes and Apparatus Therefor. In that application a uniform positive charge is placed on the surface of a xerographic plate comprising a conductive substrate coated with photoconducting material, such as amorphous selenium. The image of a document is projected onto the xerographic plate, the light areas of the document discharging the electric charge immediately thereabove and leaving only electric charges in the areas corresponding to dark areas of the document.

A desired dielectric material, examples of which will be discussed hereinafter, is backed by a conducting backing surface element and sensitized by charging uniformly at a polarity opposite to the polarity of the electric charge on the xerographic plate. The dielectric material is superimposed in darkness over the image bearing xerographic plate with the photoconductive material of the plate and the dielectric in contact without any direct electric connection between the photoconductive backing elements. The conductive backing elements are then electrically interconnected and the image is transferred by separating the plates while they are maintained at a predetermined direct potential difference. An electrostatic charge pattern corresponding to the initial image has thus been formed on the dielectric layer such that the image and background charges are of opposite polarity, a condition which is particularly desirable for obtaining high contrast in development.

As shown in FIG. 1, the dielectric material, as charged with respect to the conducting backing surface element 12, is placed in a print frame comprising a box-like structure forming a chamber 16 connected to a tank 18 containing a solvent 20, the vapors of which flow through a conduit 22 with the valve 24 open, as shown, to the chamber 16. A heater 26 is provided to insure vaporization of the solvent 20, although in some instances heat will not be required. Positive movement of the vapor is aiforded by a blower 28 which also serves, when the valve 24 is thrown to close the conduit 22, to force clear air into the chamber 16 and purge. the excess vapor from the film 10 to fix it. Excess vapor is forced through conduit 30 into a condenser 32, having a vapor trapping air vent 34, to return condensed solvent through conduit 36 to the tank 18.

lfdesired, the fixed film image may be erased merely by placing an uncharged film bearing a distortion image in ing with clear air. of the deformation image.

Only one to two seconds developing time is required for an image to be developed orerased from polystyrene plastic by placing it in a tank containing trichlorethylene vapors. Since the soluplastic material is softened progressively inward from the surface by action of the solvent vapor, improved image resolution is obtained with faster more easily controllable development. Important in automatic processing machines is the fact that the strength of the soluplastic isnot greatly impaired, whereby the Web may be pulled through a machine without substantially distortingthe developing image.

Examples of dielectric material suitable for use are: Polystyrene, polymethylmethacrylate, polyvinylchloride, polyvinylidene chloride, ethylcellulose and styrene coated polyethylene terephthalate. Examples of solvents suitable for use are: Trichloroethylene, acetone, toluene, and methylene chloride.

Thus far the techniques of the invention have been described as a stepwise process performed with flat surface structural elements. Continuous processing is possible with the techniques and one such arrangement according to the invention is shown in FIG. 2. Only the essentials are shown in this illustration, it being understood that conventional methods and structures for transporting the various components of the appartus, shielding the charged areas from light or electrostatic fields, sealing the vapor and solvent, and the like, are readily apparent to those skilled in the art. In a vapor and light tight housing 4%, a continuous web 10 of dielectric, unwinding from a supply reel 44 and winding on a storage reel 46, is carried over guide rollers as necessary. At a point where the web 10' passes over a conductive drum 47, which is maintained at fixed reference potential, preferably ground as shown, the web 10' is given a uniform negative charge by means of a corona charging unit 48. A drum conveniently completely metallic but at least having a conductive peripheral surface element 51 maintained at ground potential, as shown, and having a charge image recording layer, for example of amorphous selenium, thereon is arranged to be charged positively by means of a corona charging unit 52. A pair of direct potential supplies 54 and 56 are arranged to energize the corona charging units 48 and 52 with potentials of opposite polarity.

Images on a continuous web of document-s 60 (or on single documents inserted and removed by hand, one after the other into a feeding slot 62), illuminated by synchronized slit exposure system indicated only schematically by a pair of lamps 64 are produced in succession as charged images on the selenium drum 5th in more or less conventional manner. Insulating rollers 66 and 67 urge the web into contact with the xerographic drum 50. Another drum 68 is arranged to back the Web 10' at the point on the xerographic drum 50 where the charge transfer process takes place. This backing drum 68 has at least a peripheral conductivesurface element 69 forming the backing conductive surface element of the .dielectric web 10 during the transfer process and preferably connected to the shaft on which the backing drum d3 rotates as shown. The conductive surface element 6% on the backing drum 68 is electrically insulated from the remainder of the structure and connected to an aiding potential source 70, delivering from zero to several thousand volts direct potential as predetermined. A suitably housed lamp 71 is arranged to discharge the image charge remaining on the selenium coating aftercharge transfer.

The soluplastic web 10" bearing a charge pattern corresponding to the desired image tobe recorded is next passed around a drum 72 having at least a conductive peripheral surface 74 forming in conjunction With-a manifolding arrangement a developing chamber 16' and a purging chamber 16 A vapor tight seal'76 is arranged, around the edge of the manifolding arrangement so 'that vapor does not escape. While. a vapor tight seal i is desirable between the two chambers, baffle means '78 are sufficient to prevent a large amount of vapor from the "developing chamber 16'. from getting into the purgin chamber l6. Separate conduits 82 and 84 are arranged to return excess vapor to the condenser 32. Otherwise the structure is much the same as that shown in FIG. 1, save for the important feature that a separate developing chamber lid and a separate purging chamber 16" receive the dielectric film web 19' as it passes through the developing and fixing processes. The web ltl bearing a deformation image is that wound on the storage reel 46 for future use.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that many changes in the form and details may be made there-v in without departing from the spirit and scope of the invention.

The invention claimed is:

1. Apparatus for producing deformation images on dielectric material soluble in a chemically related solvent and having an electrostatic charge pattern thereon, comprising, 7

means for transporting said dielectric material,

means associated with said transporting means for forming a pair of vapor sealed chambers contiguously of said transporting means,

means for guiding said charged dielectric material to said transporting means and through said chambers in succession,

a tank containing liquid solvent, I

means arranged in said tank for vaporizing said solvent,

a manifold connecting said tank to said chambers,

solvent vapor condensing means interposed in said manifold between said chambers and said tanks, and pressurizing means inter-posed in said manifold for forcing vapor of said solvent into the first chamber for softening said dielectric material and deforming it in accordance with the electrostatic stresses of the charge patterns thereon and for forcing an excess of said vapor into said condensing means and for forcing vapor out of said second chamber and into said condensing means for permitting said deformed dielectric material to V harden and for returning excess solvent to said tank.

2. Apparatus for producing deformation images on di-- electric material soluble in a chemically related solvent and having an electrostatic charge pattern thereon, com prising,

a rotatable drum, means associated with said drum for forming a pair of vapor sealed chambers circumferentially of said drum, means for guiding said charged dielectric material over said drum through said chambers in succession, a tank containing liquid solvent, means arranged in said tank for vaporizing said solvent, a manifold connecting said tank to said chambers, solvent vapor condensing means interposed in said manifold between said chambers and said tank, and pressurizing means interposed in said manifold for forcing vapor of said solvent into the first chamber for softening said dielectric material and deforming it in accordance with electrostatic stresses of the charge patterns thereon and for forcing an excess of said vapor into said condensing means and-for forcing vapor out of said second chamber and into said condensing means for permitting said deformed dielectricmaterial to harden and for returning excess sol-- vent to said tank. Y i f 3. Apparatus for producing deformation images on dielectric material soluble in a chemically related solvent, comprising,

means for establishing electrostatic charge patterns on 1 said dielectric material,

ance with said electrostatic charge patterns, said means comprising,

a rotatable drum,

means associated with said drum for forming a pair of vapor sealed chambers circumferentially of said drum,

means for guiding said charged dielectric material over said drum through said chambers in succession,

a tank containing said solvent in liquid state,

means arranged in said tank for vaporizing said liquid solvent,

a manifold connecting said tank to said chamber,

solvent vapor condensing means interposed in said manifold between said chambers and said tank, and

pressurizing means interposed in said manifold for forcing vapor of said solvent into the first chamber for softening said dielectric material and deforming it in accordance with the electrostatic stresses of said charge patterns thereon and for forcing an excess of said vapor into said condensing means and for forcing vapor out of said second chamber and into said condensing means for permitting said deformed dielectric material to harden and for returning excess solvent to said tank.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES T.P.R. Recording, A Reprint in Electronic Industries pp. 76-79 Feb. 1960, Phila., Pa. 

1. APPARATUS FOR PRODUCING DEFORMATION IMAGES ON DIELECTRIC MATERIAL SOLUBLE IN A CHEMICALLY RELATED SOLVENT AND HAVING AN ELECTROSTATIC CHARGE PATTERN THEREON, COMPRISING, MEANS FOR TRANSPORTING SAID DIELECTRIC MATERIAL, MEANS ASSOCIATED WITH SAID TRANSPORTING MEANS FOR FORMING A PAIR OF VAPOR SEALED CHAMBERS CONTIGUOUSLY OF SAID TRANSPORTING MEANS, MEANS FOR GUIDING SAID CHARGED DIELECTRIC MATERIAL TO SAID TRANSPORTING MEANS AND THROUGH SAID CHAMBERS IN SUCCESSION, A TANK CONTAINING LIQUID SOLVENT, MEANS ARRANGED IN SAID TANK FOR VAPORIZING SAID SOLVENT, A MANIFOLD CONNECTING SAID TANK TO SAID CHAMBERS, SOLVENT VAPOR CONDENSING MEANS INTERPOSED IN SAID MANIFOLD BETWEEN SAID CHAMBERS AND SAID TANKS, AND PRESSURIZING MEANS INTERPOSED IN SAID MANIFOLD FOR FORCING VAPOR OF SAID SOLVENT INTO THE FIRST CHAMBER FOR SOFTENING SAID DIELECTRIC MATERIAL AND DEFORMING IT IN ACCORDANCE WITH THE ELECTROSTATIC STRESSES OF THE CHARGE PATTERNS THEREON AND FOR FORCING AN EXCESS OF SAID VAPOR INTO SAID CONDENSING MEANS AND FOR FORCING VAPOR OUT OF SAID SECOND CHAMBER AND INTO SAID CONDENSING MEANS FOR PERMITTING SAID DEFORMED DIELECTRIC MATERIAL TO HARDEN AND FOR RETURNING EXCESS SOLVENT TO SAID TANK. 